1. Field of the Invention
This invention relates to a road traffic information processing apparatus installed in a system that can display road conditions, typified by an in-vehicle navigation system, a road traffic information processing method, a program for causing a computer to function as the road traffic information processing apparatus, and an information record medium recording the program.
2. Description of the Related Art
A road traffic information communication system (Vehicle Information Communication System) using FM multiplex telecasting and beacons installed on roads for transmitting and receiving various pieces of road traffic information indicating traffic jam conditions, traffic control conditions, etc., is developed. A road traffic information processing apparatus for serving as a receiver for receiving the road traffic information is installed in most recent in-vehicle navigation systems.
The in-vehicle navigation system contains storage means (storage medium) storing map data made up of a large number of pieces of information such as road data and facility data, and reads the regional map on the periphery of the current position of the vehicle or the regional map of the region to be checked by the user from the storage means, and displays the map on display means implemented as a liquid crystal display, etc.
Further, the in-vehicle navigation system installing a road traffic information processing apparatus can also superpose information indicating the road conditions from time to time on the map for display based on various pieces of road traffic information received, so that the driver can check the road conditions changing every moment while seeing the map.
FIG. 7 schematically shows the principle structure of road data contained in the map data. The road data has the basic configuration of combinations of links and nodes. The link means a line connecting an intersection on a road and another intersection adjacent to that intersection via the road and is given a link number, etc., for management; in FIG. 7, the links are represented as L1, L2, L3 . . . The node is a point connecting two or more links and is given a node number, etc., for management; in FIG. 7, the nodes are represented as N0, N1, N2 . . . Two node information pieces and the link information connecting the nodes make up the above-mentioned basic configuration as one road unit. Further, the road unit contains information called traffic information link aside from the links L1, L2, L3 . . . and is represented as v1 or v2 in FIG. 7.
As seen in the figure, in this example, at least two traffic information links are contained corresponding to one link. The traffic information links are provided corresponding to lanes headed in opposite directions; for example, the traffic information link numbers are given in such a manner that v1 and v2 are given to up and down lanes, respectively, of a main national load or that v1 and v2 are given to inner and outer lanes, respectively, of a two-way belt expressway.
Road traffic information transmitted in the road traffic information communication system is limited to that of the main roads at present, and information concerning all roads is not yet transmitted. Thus, in the above-mentioned map data, the traffic information links are provided only for the road units corresponding to the traffic information transmitted in the road traffic information communication system; for example, no traffic information links are provided for road units corresponding to roads whose traffic information is not transmitted like the road unit containing the link L7 in FIG. 7.
The traffic information transmitted in the road traffic information communication system is made up of at least link number information, traffic information link number information, road condition information, and condition section information. The road condition information contains traffic jam information and control information as condition types so that the traffic conditions of actual roads can be differentiated from each other for recognition. Further, the traffic jam information is classified into information of types responsive to the traffic jam degree such as “heavy traffic jam” and “congestion” and the control information is classified into information of types responsive to the control contents such as “closed to vehicles” and “speed regulation”. The condition section information indicating the road section where a traffic jam occurs and the controlled section contains occurrence start position information and occurrence section information of each occurrence section. The occurrence start position information is distance information from the start point in the travel direction of the vehicle in traffic information link; for example, if the distance information indicates 0 meters, the start point of the traffic information link is assumed to be the start position of the occurrence section and if the distance information indicates 200 meters, the point at a distance of 200 meters from the start point of the traffic information link is assumed to be the start position of the occurrence section and the traffic jam or control (regulation) continues following the position in the travel direction. The occurrence section information (traffic jam distance, etc.,) of the section where the traffic jam or control occurs is distance information from the start position.
Upon reception of road traffic information by the road traffic information processing apparatus installed in an in-vehicle navigation system, the in-vehicle navigation system superposes arrows generated based on the road condition information and the condition section information on the map along the road displayed based on the road data contained in the map data for display, as shown in FIG. 8. In the example in the figure, the road traffic information processing apparatus receives the road condition information indicating a heavy traffic jam concerning traffic information link v1 of link L2, traffic information link v1 of link L4, and traffic information link v1 of link L10, receives the road condition information indicating congestion concerning traffic information link v1 of link L3, and further receives the road condition information indicating control concerning traffic information link v2 of link L10; the arrows are displayed in response to the road condition information and the condition section information in the information. In the figure, for convenience of the description, the links, the traffic information links, and the nodes are represented by dashed lines, but only roads and arrows represented by solid lines are displayed on display means of an actual navigation system.
In the example, in the heavy traffic condition concerning the road indicated by link L2 and the congestion condition concerning the road indicated by link L3, a heavy traffic jam or congestion does not occur in all area and occurs from the point at a predetermined distance relative to each forward intersection.
As seen in the figure, a current position mark P indicating the current position of the vehicle is displayed on the road map, whereby approach to a traffic jam section or a control section or the like can be checked in comparison with the position of the vehicle. The current position of the vehicle can be provided by a known current position detection apparatus made up of a GPS receiver, a gyro sensor, a vehicle speed pulse detector, etc.
The in-vehicle navigation system has a function of calculating the route to the destination set by the user and aiding in guiding the vehicle along the determined route. For example, it is made possible to produce voice output such that “turn to right at XX intersection meters ahead” for prompting the driver to make a turn at the intersection. Further, the in-vehicle navigation system installing a traffic information receiver has a function of notifying the driver of the conditions and the section if traffic jam information or control information exists on the route along which the vehicle is guided upon reception of road traffic information. For example, the in-vehicle navigation system produces voice output such that “XX-kilometer traffic jam occurs ahead.”
The notifying function faithfully informs the driver of the received road traffic information about the first encountered traffic jam or control when the vehicle runs along the route. For example, in FIG. 8, it is assumed that a route passing through links L1, L2, L3, and L4 in order is set as the route to the destination. A notification based on the traffic information link v1 of the link L2 is made at a predetermined timing when the vehicle runs on the link L1. The vehicle further moves and a notification based on the traffic information link v1 of the link L3 is made at a predetermined timing when the vehicle runs on the link L2. Likewise, a notification based on the traffic information link v1 of the link L4 is made at a predetermined timing when the vehicle runs on the link L3.
Thus, to faithfully inform the driver of the received road traffic information, the driver is notified of the information for each traffic information link at each corresponding timing.
On the other hand, if the driver visually checks these information pieces through the display means of the in-vehicle navigation system, even if the traffic jams are separate, the drive may recognize the traffic jam as a visually continuous traffic jam to no small extent. That is, in the example, as the visually checked sections, the road traffic information concerning the traffic information links of the links L2, L3, and L4 is recognized as a continuous heavy traffic jam or congestion. However, only the notification based on the traffic information link of the link L2 is made from the voice output as described above and consequently the user may recognize the visually checked information and the information provided from the voice output as different information.